WebSubmit: better value escaping

* More complete escaping of values using `escape_javascript_string`
  from htmlutils.  (closes #1578)

Signed-off-by: Jerome Caffaro <jerome.caffaro@cern.ch>
WebSubmit: value escaping for modifications

* Escape the values to display for appropriate insertion
  into HTML/Javascript.  (addresses #1578)

Signed-off-by: Jerome Caffaro <jerome.caffaro@cern.ch>
WebSubmit: new Create_Modify_Interface parameters

* Adds new parameters 'prefix', 'suffix', 'button_label',
  'button_prefix' and 'dates_conversion' to WebSubmit function
  Create_Modify_Interface for increased customizability of the
  interface.

Signed-off-by: Jerome Caffaro <jerome.caffaro@cern.ch>